This study describes some of the most important swelling characters of expansive soils when used
as foundation materials to support various types of civil engineering structures. Expansive soils are considered
among difficult foundation materials and expand upon wetting and shrink upon losing moisture. They are
considered problematic soils for architectural and civil engineers. These types of soils may cause minor to
major structural damages to pavements as well as buildings. It is therefore essential to detect swelling soils from
non-problematic foundation soils before any civil engineering projects are constructed over or adjacent to them.
The study begins with definition of expansive soils and shows its distributions in the world as well as the basic
causes for swelling potential that these type of soils poses. It is also shown that, the most probable depth of
expansion to check for possible swelling potential for swelling soils is soilís active zone. This zone is the most
upper depth of expansive soil and it may extend up to 20 ft. (6 m) below ground level. The moisture content
of soil through active zone varies during different seasons while in lower part of expansive soil the moisture
content stays constant during hot and cold season. Among various methods to check for swelling potential,
plastic index and liquid limits are two most crucial factors, as these factors tend to increase, the swelling
potential increase as well.